The purpose of the proposed research is to clarify the role of collagen metabolism in the pathogenesis of atherosclerosis. Arterial collagen biosynthesis will be measured at specific time intervals during the progression of atherosclerosis in dogs maintained on a diet previously shown to be atherogenic when fed for one year. Alterations in the rate of collagen synthesis as measured in vitro through incorporation of isotopically labeled proline into collagen hydroxyproline will be correlated with changes in prolyl hydroxylase activities to determine whether the activity of this enzyme is the major rate-limiting factor in collagen synthesis as has been frequently claimed, though never proven. Sequential changes in collagen metabolism will also be followed in canine arterial intima-media during various stages of lesion regression. Vasoactive compounds have been shown to increase endothelial permeability by various means. The effects of angiotensin, histamine, norepinephrine, epinephrine, serotonin, bradykinin and isoproterenol on collagen synthesis in isolated arterial preparations and in cultures of smooth muscle and endothelial cells will be investigated. The object of these studies is to establish whether vasoactive compounds in "physiological" concentrations can stimulate collagen synthesis. A major objective of this proposal is to test the hypothesis that in addition to enhanced rates of collagen synthesis in atherosclerotic plaques or in areas susceptible to the development of sclerotic lesions, there are specific changes in the genetic types of collagen being synthesized and a basic alteration in intimal cell differentiation. The relationship of changes in differentiated function to enhanced rates of collagen synthesis and furthermore to the preferential synthesis of one type of collagen over another, as suspected from our preliminary studies in human arterial plaques, will be investigated.